As disclosed in early known arts, for example, U.S. Pat. Nos. 3,869,429 and 3,869,430, wholly aromatic polyamide filaments are manufactured by a series of processes including: a process of preparing wholly aromatic polyamide polymer by polymerizing aromatic diamine and aromatic diacid chloride in a polymerization solvent containing N-methyl-2-pyrrolidone; a process of preparing a spinning liquid dope by dissolving the prepared polyamide polymer in a concentrated sulfuric acid solvent; a process of forming filaments by extruding the spinning liquid dope through spinnerets and passing the spun material through a non-coagulation fluid layer into a coagulant tank; and a process of refining the resulting filaments by washing, drying and heat treatment processes.
FIG. 1 is a schematic view illustrating a conventional method of manufacturing wholly aromatic polyamide filament by general known dry-wet spinning process.
As to the conventional process illustrated in FIG. 1, since the spun material is fed into a coagulation tank 50 through the non-coagulation fluid layer and coagulated in the tank, surface of the spun material is coagulated faster and more than inside thereof, thereby causing a problem that physical properties of the surface and inside of the spun material are irregular and different from each other. Accordingly, in case of applying a high spinning and take-up velocity, a lot of cut threads and/or staples are typically generated, thus, it is not possible to increase the spinning and take-up velocity above 600 m/min.
Such limitation of the spinning and take-up velocity affects the final product, that is, wholly aromatic polyamide filament, so as not to have the strength and modulus improved above desired levels and creates a problem in raising productivity thereof.
Meanwhile, Korean Patent Laid-Open No. 1995-934 proposes a process of manufacturing wholly aromatic polyamide fiber that arranges two injection nozzles in a coagulant tank 50, and injects water or aqueous sulfuric acid solution to spun material through one of the nozzles which is mounted on the upper part while injecting water to the spun material through the other nozzle which is positioned on the lower part of the tank.
However, the above process does not use a recycling system to recover and reuse the coagulant, leading to rising in production costs and causing environmentally serious contamination.
Moreover, since this process is not subject to application of a mechanism for controlling injection velocity dependent on dilution level of sulfuric acid in the coagulant, it has a disadvantage in that the surface and inside of the spun material are unable to be evenly and uniformly coagulated.
As a result of intensive study and investigation made by the present inventor in order to solve the foregoing conventional problems, the present invention has been suggested to produce novel wholly aromatic polyamide filament with improved strength and modulus with reasonable cost and without environmental contamination.